Silicone balloon catheter

ABSTRACT

The present invention includes an improved configuration and method of forming an inflatable silicone balloon on a cured silicone catheter that does not require a release agent to free the balloon from the catheter. The method includes a catheter having an inflation lumen therein and an inflation port on the distal end thereof communicating the inflation lumen with the outer surface of the catheter within the interior of the balloon, comprising the following steps: 
     Providing a substantially cured silicone compound sleeve having an inner diameter corresponding to the outer diameter of the catheter and having a length corresponding to the desired length of the inflatable balloon. Positioning the sleeve onto the distal end of the catheter and centered on the inflation port. Overdipping the distal end of the catheter and the sleeve into an uncured silicone dispersion compound to a depth of about 0.25 inches beyond the sleeve, forming an uncured silicone compound layer over the catheter and the sleeve. Drying the silicone compound layer on the sleeve and catheter. 
     Next, Curing the silicone compound layer and the sleeve on the catheter, whereby the compound layer is securely bonded to the outer surface of the catheter and is bonded to the outer surface and ends of the sleeve, and the inner surface of the sleeve does not bond to the surface of the catheter. 
     Finally, releasing the inflatable balloon portion from the catheter, by applying a slight lateral force to the surface thereof, whereby the inner surface of the sleeve is translated a slight distance relative to the surface of the catheter to thereby separate any residual adhesion of the surfaces.

BACKGROUND OF THE INVENTION

The invention relates to catheters for medical and surgical procedures;particularly to improvements in silicone catheters having an expandablesilicone balloon on the distal end thereof to facilitate the removal ofthrombus (clots) or gall stones from a vessel, for occluding a vessel orfor securing the catheter within a vessel for the irrigation or drainageof fluid through the catheter.

A catheter known as an embolectomy catheter is used to remove emboli andthrombus from the veins and arteries of the body. These emboli typicallyform around the valves of the heart as a small clot that is dislodgedand follows the blood stream into the extremities of the body. The clotsare particularly dangerous if transmitted to the brain and can result ina stroke. The emboli more typically become lodged in small peripheralarteries, and in the stationary location, the clot is referred to as athrombus. Emboli can also form in the veins of the body where they tendto lodge as thrombus around the venous valves. The thrombus eventuallyincreases in size to block the vessel and are usually required to beremoved. The location of the clot is determined using fluoroscopy, andan incision is made in the major vessel near the surface having a branchleading to the clotted portion of the vessel. The embolectomy catheterwith the balloon deflated is inserted through the incision and along thevessel until the distal tip is carefully moved through the clot. Theballoon is then inflated on the distal side of the clot and the catheteris gradually withdrawn; and the clot is removed at the point of theincision, and the vessel is restored. The strength, durability andintegrity of the balloon is critical to the procedure.

A catheter known as a biliary catheter functions similarly to that ofthe embolectomy catheter and is utilized in the removal of gall stonefrom the biliary tract. The balloon is used to force the gall stonesalong and out of the tract and therefore the reliability, strength anddurability of the balloon is critical to a successful procedure.

Another type of silicone catheter known as a Foley catheter, is used forinsertion in the urethra and consists of a tube containing a primarylumen for flushing or drainage of an appropriate fluid through thebladder. The tube includes a secondary inflation lumen for inflation ofa balloon at the distal end thereof for anchoring the catheter insidethe vessel of the patient. Once the tube is anchored, body fluids can bedrained or therapeutic fluids can be injected into the body through theprimary lumen. When the catheter is no longer needed, the balloon isdeflated by releasing the inflation fluid and the catheter is withdrawnfrom the body. The function and reliability of the balloon is criticalto the successful use of such catheters.

Another type of silicone balloon catheter, known as an occlusioncatheter, is used by insertion of the catheter into a desired locationof a vessel then expanding the balloon to occlude the vessel and blockthe flow of blood or other fluid from passing through the vessel. Theonly proposed use of this type of catheter is dependent on thesuccessful inflation, expanded integrity and deflation of the balloon,so the reliability and quality of the balloon is of the ultimateimportance.

Although the basic design of such catheters has been used for a numberof years, serious problems remain with the design, manufacture andperformance of the balloon. One of the principal problems in manufacturehas been the means of reliably securing the ends of the inflatableballoon to the catheter shaft while its mid section is reliably free todistend symmetrically when inflated. In addition, the outer surface ofthe balloon must be substantially smooth and unobstructed when deflatedto facilitate insertion and removal of the catheter, and when in use,the inflated balloon must be strong and durable to ensure that it doesnot separate from the shaft, tear or leak under the fluid pressures andforces on the balloon during medical and surgical procedures. Forexample, in U.S. Pat. No. 3,734,100 issued to Walker et al., catheterconstruction is described in which a separate cuff portion is glued atits shoulders to the surface of the catheter. Although the patentillustrates the exterior surface of the catheter as being smooth andregular, in practice the thickness of the cuff portion and the effectsof the glue cause surface irregularities at the cuff's shoulder. Thus,in a typical catheter produced by a gluing process, the shoulders of thecuff will protrude beyond the remaining exterior surface of the catheterand impede the insertion or withdrawal of the catheter and increase thediscomfort to the patient. More importantly, even when properlyassembled, the gluing of the separate shoulders does not produce areliable bond of the separate balloon material to the catheter; and thetedious by-hand process causes additional imperfections and defectswhich result in an unreliable bond. Such gluing and solvent weldingprocesses resulted in a high scrap rate in manufacturing and catheterswhich do not reliably function during medical and surgical procedures.

Another process for bonding a balloon to a catheter involves a heatsealing method to weld the shoulders of a separate balloon to thesurface of the catheter. This process is an improvement over gluing, butit does not produce a durable bond, and the catheters do not reliablyfunction during medical procedures.

As an alternative, a process was developed in which the balloon materialwas formed directly onto the catheter. In this process, the exterior ofthe catheter tube in the area underlying the bubble of the balloon iscovered with a masking (release) material, and then the tip of thecatheter including the masked, bubble region is coated with a flexibleinflatable material (in liquid state), and after the bonded balloonmaterial is solidified, the underlying masking material is desolved orotherwise removed to provide the bubble portion of the balloon. Thisprocess results in good smooth bonds of the shoulder of the balloon tothe catheter but presents problems in releasing the bubble portion ofthe balloon from the surface of the catheter. For example, in thepatents to Harautuneian (U.S. Pat. Nos. 3,292,627 and 3,304,353) the useof a water soluble masking material is suggested; However, there areseveral problems with this design. In simultaneously removing the watersoluble release material and inflating the anchoring bubble,difficulties in the dissolution of the release material frequently causeparticles to become lodged in the inflation lumen preventing furtherexpansion of the anchoring bubble. Similarly, as discussed inHarautuneian's U.S. Pat. No. 3,452,756, the masking layer may onlydissolve in the localized area adjacent the hole to the inflation lumen.Thus the anchoring bubble may expand preferentially in that area andcause localized pressure injurious to the body tissue.

Similarly, U.S. Pat. No. 3,544,668 issued to Dereniuk illustrates theuse of a gel as a masking layer beneath the anchoring balloon. Followingthe formation of the outer skin on the catheter, the gel layer isvolatilized by heat. This method is difficult to practice because theouter covering of the catheter must be applied before the releasecoating has dried or is touched.

An improvement in the area of plastic balloons and plastic catheters isdescribed in U.S. Pat. No. 3,739,674 issued to Dereniuk et al. in whicha plastic catheter is coated with a release agent, then a plastic sleeveis placed over the release agent and overdipped into a plastic solutionto form a skin which adheres to the sleeve and the shaft but the releaseagent causes the inner surface of the sleeve to remain separate from theshaft.

A difficulty encountered with the prior art processes for manufacturinga plastic balloon catheter is that they are not applicable to siliconerubber, which is generally considered to be the most useful cathetermaterial. It has been found that silicone is more compatible with humantissue than previously used latex rubber and plastic materials and thatthe incidence of infection in the body tissues is appreciably reducedwith silicone catheters. In addition, thermoplastic balloons, followinginflation, do not revert to their original shape and size whichprecludes non-destructive manufacturing quality testing and operatingroom confirmation testing prior to use. Furthermore, polyurethaneballoons are unsuitable for certain in vivo uses because urinehydrolyzes polyurethane. Accordingly, it is preferable to construct theentire catheter of silicone. However, it is difficult to apply thecoatings taught by the Harautuneian and Dereniuk patents to siliconebecause of the hydrophobic property of silicone. Thus in addition to theproblems generally encountered with water soluble or volatile releasecoatings, they are not useful in processing silicone balloons onsilicone catheter.

U.S. Pat. No. 3,983,879 further discusses that silicone is morecompatible with body tissues than the thermoplastic materials, anddiscloses a method for making a silicone rubber balloon catheter. In theprocess described in this patent, a layer of thermoplastic tape is firstwrapped around the silicone catheter and covers the inflation hole, theinflation hole being the hole which leads to the catheter's inflationlumen. The tape serves to prevent adherence of the silicone balloonlayer to the catheter tubing when the tubing is dipped in a solution ofthe silicone material which forms the balloon layer. Following theformation of the balloon layer, the hole is re-opened through the tapewith a hot probe. This process is complex, costly, requires precisionlabor, and is subject to error particularly at the stage where the probeis used to re-open the inflation hole. The tape also forms annularshoulders at the respective ends of the wrappings which can causepatient irritation as well as difficult catheter withdrawal andinsertion during in vivo catheter use. Re-opening of the hole with thehot probe can result in a weak spot in the balloon layer as the probemay be passed through the balloon layer.

Additional improved silicone balloon catheters are described in U.S.Pat. Nos. 4,670,313 and 4,690,844 to Saudagar in which various partingagents are disclosed for the release of a silicone balloon from asilicone catheter. The parting agent Polyvinyl pyrrolidine isparticularly suggested for separating a silicone balloon from a siliconecatheter; additional parting agents described to be suitable for thispurpose are polyvinyl alcohol, methycellulose, starch derivatives anddextrose.

The various liquid, powder and gel chemical release agents are verydifficult to be precisely controlled in chemical composition, difficultto be precisely applied to the desired areas on the silicone catheter,difficult to be controlled from contaminating and releasing areas on thesilicone catheter on which the balloon should be bonded, difficult to bestabilized in position during the overdipping of the release agent bythe silicone compound solution, and thus are generally difficult to usein the manufacture of silicone balloon catheters. Another problem withsuch release agents is that the release agent itself remains within theinterior of the balloon which can block and clog the inflation/deflationlumen, and if the balloon bursts, tears, or separates from the catheter,the release agent chemicals and solid particles can be introduced intothe body of the patient. It is concluded that the prior art designs andprocesses for manufacturing a silicone inflatable balloon on a siliconecatheter are difficult and costly to produce and are not functionallyreliably in use during medical and surgical procedures.

In view of the foregoing, it is an object of the present invention toprovide an improved silicone balloon catheter design and process whichdoes not utilize glue, solvent or heat seals to bond the shoulder of theballoon, or release agents to form the inflatable portion of the balloonon the catheter.

It is another object to provide an improved silicone balloon catheterdesign and process which can be efficiently and reliably manufacturedand tested.

It is another object to provide an improved silicone balloon catheterwhich is functionally reliable and durable in medical and surgicalprocedures.

SUMMARY OF THE INVENTION

The foregoing objects are accomplished by an improved catheter designand method of forming an inflatable silicone balloon on a cured siliconecatheter utilizing a substantially cured sleeve to form the innersurface of an inflatable balloon. The inventors have been manufacturingand experimenting with silicone compounds and catheters for a number ofyears. They found that a substantially (but not fully) cured siliconecompound layer or a substantially (fully) cured silicone compound layercould be positioned on cured silicone material and exposed to a curingenvironment without either of the silicone compound layers beingsecurely bonded to the cured silicone material. They also found that alayer of uncured elastomeric silicone compound layer applied over asubstantially (but not fully) cured silicone compound material or asubstantially (fully) cured silicone material would be securely bondedto the surface of both materials when exposed to a curing environment.This discovery led to experimentation and the development of thesilicone balloon catheters utilizing a substantially cured siliconesleeve of the present invention as described below.

The present invention includes an improved method of forming aninflatable silicone balloon on a cured silicone catheter, with thecatheter having an inflation lumen therein and an inflation port on thedistal end thereof communicating the inflation lumen with the outersurface of the catheter within the interior of the balloon, comprisingthe following steps:

providing a substantially cured (at about 125° for about 30 minutes)silicone compound sleeve having an inner diameter corresponding to theouter diameter of the catheter and having a length corresponding to thedesired length of the inflatable balloon;

positioning the sleeve onto the distal end of the catheter and centeredon the inflation port;

overdipping the distal end of the catheter and the sleeve into anuncured silicone dispersion compound to a depth of about 0.25 inchesbeyond the sleeve, whereby the sleeve seals the inflation port and outersurface of the catheter from contact with the compound, forming anuncured silicone compound layer over the catheter and the sleeve;

drying the silicone compound layer on the sleeve and catheter (at about70° C. for about 20-30 minutes);

curing the silicone compound layer and the sleeve on the catheter (atabout 125° C. for about 45-60 minutes), whereby during curing, thecompound layer is securely bonded to the outer surface of the catheterand is bonded to the outer surface and ends of the sleeve, and the innersurface of the sleeve does not bond to the surface of the catheter; and

Finally, releasing the inflatable balloon portion from the catheter, byapplying a slight lateral force to the surface thereof, whereby theinner surface of the sleeve is translated a slight distance relative tothe surface of the catheter to thereby separate any residual adhesion ofthe surfaces. The releasing step completes the forming of the inflatablesilicone balloon over the length of the sleeve, that is securely bondedto the catheter which can be reliably inflated and deflated by pressureapplied at the proximal end of the inflation lumen.

The present invention also includes a design for utilizing the foregoingmethod and a resulting improved silicone catheter having an inflatablesilicone balloon on the distal end thereof, comprising a cured siliconecatheter, a silicone compound inner sleeve and a silicone compound layerforming the outer layer of the balloon. The catheter has at least oneinflation lumen therein and at least one inflation port on the distalend thereof. A key feature of the invention is the inner balloon sleeveformed of a substantially cured silicone compound having an innerdiameter corresponding to the outer diameter of the catheter and havinga length corresponding to the desired length of the balloon. The sleeveis positioned onto the distal end of the catheter and centered on theinflation port. An initially uncured silicone compound layer is formedon the distal end of the catheter, and over the outer surface and endsof the sleeve and having a length extending beyond the ends of thesleeve, whereby the silicone compound does not contact the inner surfaceof the sleeve. Whereas in the cured configuration, the silicone compoundlayer is securely bonded to the outer surface of the catheter and issecurely bonded to the ends and the outer surface of the sleeve, and theinner surface of the sleeve is not bonded to the outer surface of thecatheter. The inner surface of the sleeve is adapted to be released fromany adhesion with the catheter by a slight lateral force on theperiphery of the layer over the sleeve, and thereby forms the inflatablesilicone balloon on the silicone catheter.

BRIEF DESCRIPTION OF THE DRAWINGS

While the novel features of the invention are set forth in the appendedclaims, the invention will be better understood along with otherfeatures thereof from the following detailed description taken inconjunction with the drawings, in which:

FIG. 1 is a side elevational view of a typical silicone catheter of thepresent invention, with the distal end thereof sectioned to illustratethe interior lumens of the catheter;

FIG. 2 is a sectional view taken along 2--2 of FIG. 1 and typical of a2-3 Fr. size catheter;

FIG. 3 is a view similar to FIG. 2 and typical of a 4 Fr. size catheter;

FIG. 4 is a view similar to FIG. 2 and typical of a 5 Fr. and largersize catheter;

FIG. 5 is a side elevational view of a sleeve utilized in forming aninflatable balloon on the catheter;

FIG. 6 is a side elevational view partially sectioned to illustrate thecatheter with the sleeve positioned thereon, and processing mandrelsinserted into the ends of the lumens;

FIG. 7 is a side elevational view of the catheter and sleeve of FIG. 6,after a first overdipping of the distal end thereof has been performed;

FIG. 8 is a side elevational view of the catheter of FIG. 7, after asecond overdipping of the distal end thereof has been performed;

FIG. 9 is a side elevational view of the catheter of FIG. 8, after thesilicone balloon has been cured,

FIG. 10 is a front elevational view of the catheter of FIG. 9 furtherillustrating an operation of a releasing tool over the inflatableportion of the balloon to separate it from the catheter;

FIG. 11 is an enlarged partial view of the catheter and tool of FIG. 10;

FIG. 12 is a side elevational view of the catheter of FIG. 9 with thedistal silicone tip added; and

FIG. 13 is a side elevational view of the catheter of FIG. 10 shownpartially sectioned and with the fully formed balloon thereof inflatedby fluid pressure through the lumen.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIGS. 1, 2, 3 and 4 there is illustrated a typicalcatheter 20 that is extruded from medical grade silicone into a desireddiameter and through a curing chamber, then cut to a desired processinglength. Embolectomy catheters for example typically have diameters of 2French (Fr.) (equal to 0.026 inch/0.66 mm), 3 Fr. (0.039 inch/1.00 mm),4 Fr. (0.053 inch/1.35 mm), 5 Fr. (0.066 inches/1.68 mm), 6 Fr. (0.079inches/2.00 mm) and 7 Fr. (0.092 inches/2.34 mm). and a length rangingfrom about 40 cm to 100 cm. The catheter includes at least one inflationlumen 22 for inflating and deflating a distal balloon (to besubsequently formed thereon); and at least one primary lumen 24 whichcan be utilized in embolectomy catheters to enclose wound stainlesssteel stiffening wires 26 to provide the desired rigidity to the ratherflexible silicone rubber catheters. It is preferable in embolectomycatheters that such stiffening wires be integrally co-extruded with thecatheters. In uretheral type catheters, the primary type lumen can beutilized with a distal fluid port (28) to deliver and withdraw fluidsthrough the primary lumen during medical procedures. The distal end ofthe catheter includes an inflation port 30 communicating each inflationlumen with the outer surface of the catheter at a location within theballoon portion of the catheter. Each inflation ports is typicallypunched into the lumen with a sharpened syringe needle, that is pushedand twisted to cut and remove the plug from the wall of the catheter.

Referring particularly to FIG. 2 a typical lumen and port configurationis illustrated for the small 2 Fr. and 3 Fr. catheters, while FIG. 3illustrates a typical configuration for size 4 Fr. catheters, and FIG. 4illustrates a typical configuration for the larger size 5 Fr. 6 Fr. And7 Fr. catheters. The larger size catheters have greater balloon surfaceand volume which require larger and multiple inflation lumens and ports,and have larger cross sections to facilitate such multiple lumens forperforming the required medical procedure. The size of the catheterselected for a specific medical or surgical procedure is usuallydependent upon the size of the vessel in which to procedure is toperformed.

Referring now to FIG. 5, there is shown a sleeve 32 that is formed of athin layer of elastomeric silicone dispersion compound that haspreferably been substantially, but not fully, cured. Alternatively, asubstantially fully cured sleeve can be successfully utilized in themethod and design of the present invention as discussed later in thespecification. The sleeve is a key element in the balloon design andmanufacturing process of the present invention.

The sleeves 32, as well as the other layers of the balloon, arepreferably produced from a silicone dispersion compound formulated froma dimethyl silicone elastomer dispersion in xylene solvent with acrosslink catalyst (ethylcyclohexanol inhibited) and available fromMentor Polymer Technologies. The formulation of such compounds cansuitably range from about 85-95% of elastomer, 5-15% solvent and about0.1-0.3% catalyst depending primarily on the desired viscosity and layerthickness. The compound is typically prepared in batches of about onethousand to three thousand grams depending upon production requirements.General manufacturing practices and quality control measures areemployed to control and confirm the design variables of the compound.Such variables include: verification of the percentage of dispersionsolids (by weighing, curing and re-weighing a sample) preferably about30-32%; confirming the desired compound formulation which, for a typical3000 gram batch, comprises preferably about 2675 gms (89.2%) ofelastomer, about 318 gms (10.6%) of xylene and about 7 gms (0.2%) ofcrosslink catalyst; and the viscosity is periodically confirmed with a1/8 inch diameter ruby ball in a Gilmont 32033 glass viscosity tube,with which a preferable viscosity corresponds to the descent of the rubyball at a rate of about 10 cm per minute; and the viscosity can beadjusted by adding or evaporating xylene within the compound. Aftercuring, the properties of the preferable compound include shore Adurometer greater than 30, tensile strength of about 1200-1500 psi, andelongation of about 650-800%.

The sleeve 32 is preferably produced by a mandrel dipping process intothe above described silicone compound. The silicone compound is preparedand placed into a stainless steel container that is mounted on aplatform that can be precisely raised and lowered at a predetermineddistance, rate and duration. A processing oven is preheated to 125°Degrees C. The balloon sleeve dipping mandrels (not shown) have a lengthof about 6 inches (15 cm) and diameters closely matched to the diametersof the corresponding catheters, as follows:

0.030 inch Diameter. mandrels for 2 F catheters

0.042 inch Diameter. mandrels for 3 F catheters

0.052 inch Diameter. mandrels for 4 F catheters

0.062 inch Diameter. mandrels for 5 F catheters

0.073 inch Diameter. mandrels for 6 F catheters

0.089 inch Diameter. mandrels for 7 F catheters

The mandrels are initially cleaned with isopropyl alcohol, and are thensecurely mounted in a dipping fixture (not shown) which is thenpositioned above the container of the silicone compound. Up to about 100mandrels may be mounted in a typical fixture. The mandrels are fixed inposition and the container of silicone compound is smoothly raised andlowered to dip the mandrels into the compound. A satisfactory sleevelayer of about 0.005 inches (0.13 mm) thickness is produced when theplatform is raised at a rate of about 0.143 inch (0.36 cm) per second,and reversed and lowered at a rate of about 0.031 inches (0.08 cm) persecond. The rate of travel of the platform can be finely adjusted toproduce sleeving having a desired wall thickness and performancecharacteristics. The mandrels and fixture are next transferred to theoven and placed into the oven in the inverted "tip down" position at125° C. for about 30-40 minutes until the sleevings are substantiallycured. The sleevings are preferably substantially cured at 125° C. forabout 30 minutes, (which subsequently results in an integral bond withouter layers of the inflatable balloon during curing, and yet has aninner surface which does not bond with the surface of the catheter andcan be reliably released from the catheter). Alternatively, if desired,the sleevings can be placed in the oven for about 40 minutes tosubstantially fully cured (which subsequently results in a less integralbond with outer balloon layers but has an inner surface which can bemore readily released from the surface of the catheter). The mandrelsare then cooled and removed from the dipping fixture. The individualmandrels are then placed in a plastic bottle and covered with "Ocotron",a freon gelosol (trichlortrifloromethene) available from Baxter HealthCare Corp., which expands the silicone sufficiently so the sleevingsreadily slide off of the mandrel. The Ocotron is dissipated from thesilicone, and the sleeving is returned to it's regular size forapproximately 20 minutes. About one-half inch is trimmed and discardedfrom each end of the silicone sleeving. The sleeving is then transferredto a suitable sleeve cutting fixture to cut each balloon sleeve 32 tolength, as follows:

0.130-0.160 inch length for 2 Fr. Catheter

0.150-0.180 inch length for 3 Fr. Catheter

0.200-0.240 inch length for 4 Fr. Catheter

0.250-0.275 inch length for 5 Fr. Catheter

0.280-0.310 inch length for 6 Fr. Catheter

0.400-0.425 inch length for 7 Fr. Catheter

The sleeves are than typically identified by size and stored incontainers with part number and lot numbers for use in manufacturing.

Referring now to FIG. 6, the proper sleeve 32 is selected for thecatheter being manufactured, and is initially placed in a dish ofisopropyl alcohol, and then gently placed over the distal end of thecatheter and positioned generally centered over the inflation port 30.The tubing and the sleeve should preferably be kept wet with alcohol toallow positioning of the sleeve without distorting or stretching of thesleeve. After positioning the sleeve over the inflation port, the sleeveshould be rotated around the tubing axis to assure against sleevedistortion as the alcohol dissipates. The catheters with sleeves are putin aluminum trays and placed into the oven to evaporate the alcohol, anddry for 10-15 minutes at 125° C.

Each catheter is further prepared for processing, which includes theinsertion of wire processing mandrels 34 to seal the distal ends of theinflation lumens 22 and any open primary lumens 24. These mandrels areabout 2-3 inches (5-7 cms) in length and have diameters closely matchedto the diameters of the lumens, for example, a 4 Fr. Catheter typicallyhas a lumen size of about 0.008 to 0.012 inch diameter and utilizes amandrel having an acceptable diameter of about 0.008-0.010 inches. Themandrels should preferably have rounded ends to avoid cutting the tubingwalls and be cleaned with isopropyl alcohol. Alcohol may be used to wetthe mandrel to facilitate insertion into the lumens but care should betaken not to wet the catheter with alcohol. Any residual alcohol tendsto degrade the quality of the silicone bonds and burst strength(durability) of the balloons.

Referring now to FIGS. 7, 8 and 9, the balloon layers are formeddirectly onto the catheter 20 by a well known "overdipping" processsimilarly to the process described in the production of the sleeving onthe mandrels. In preparation for the processing of the catheters, thesilicone dispersion compound is formulated and prepared as previouslydescribed, and a drying oven is preheated to 70° C., and a curing ovenis preheated to 125° C. As previously discussed, the distal end of thelumens are sealed by the wire processing mandrels 34, and the siliconesleeve 32 seals the inflation port and the surface of the cathetercovered by the sleeve (as illustrated in FIG. 6), and the catheter isready for farther processing.

Each catheter is securely positioned into a dipping fixture (not shown)with the distal end extended downwardly approximately three inches (7.6cm) beyond the fixture for adequate depth of dipping. The fixture istypically processed in a lot of about 100 catheters. The fixture andcatheters are next mounted on the dipping machine over the container ofsilicone compound. Similarly as the process in the production of thesleevings, the container of silicone compound is raised at a rate ofabout 0.143 inch (0.36 cm) per second, until the distal end of thecatheter and sleeve are immersed (overdipped) about 0.250 inches (0.65cm) past the sleeve to a catheter depth of about one and one-half inches(3.8 cm), whichever is greater; and then the direction of the platformis reversed and lowered at a rate of about 0.031 inches (0.08 cm) persecond. until the catheters are completely withdrawn from the siliconecompound. The catheters remain on the rack for 5-10 minutes to allow thecompound to stabilize. The fixture and catheters are carefully removedfrom the dipping machine and placed with the distal tips invertedupwardly into the 70° C. oven and dried for 20-25 minutes. The fixtureand catheters are then removed from the drying oven and allowed to coolto room temperature for about 5-10 minutes. The first overdippingprocedure with the above described silicone compound and overdippingcycle adds a silicone layer 36 of about 0.005 inch (13 mm) to thecatheter and sleeve, as illustrated in FIG. 7.

For certain balloon silicone compounds and performance specifications, asingle overdipping may be sufficient to form the desired balloon layer.However, a second overdipping layer 38, as illustrated in FIG. 8, ispreferable for suitable formation of the balloon layer of about 0.015inches (0.38 mm) for 2 Fr. and 3 Fr. embolectomy catheters, and a thirdoverdipping is preferable for the balloon layer of about 0.020 inch(0.50 mm) for 4-7 Fr. embolectomy catheters.

The second and third overdipping processes are repeated as describedabove for the additional balloon layers, except that the catheter ispreferably immersed approximately 1/16-1/8 inch. less than the previousprocess, as shown at 40 in FIG. 8. Alternatively, the additional layerscan each be immersed about one-eighth inch deeper than the previousdipping which may provide a smoother transition at the junction of theadjacent layer. However, It is preferable that the first layer 36 is thedeepest immersion because it provides a continuous layer that makes anexcellent uninterrupted bond with the surface of the catheter.

After the final silicone balloon layers have been dried, the cathetersare transferred to the curing oven and remain at 125° C. for about 45-60minutes until the silicone balloon layers are fully cured. During thecuring process, the silicone balloon layer 36 in contact with thecatheter surface becomes smoothly and securely bonded to the catheter;and the layer 36 and additional layers 38 become integrally bonded witheach other and bonded with the sleeve 32; and the transition junctions40 of the additional layers (and at the sleeve) become smoothly blendedto result in the balloon 42 as illustrated in FIG. 9. (The sleeve isshown in FIGS. 9, 12 and 13 to indicate the inflatable portion of theballoon.)

A distinction of the preferable substantially partially cured siliconesleeve over the substantially fully cured sleeve is basically, thatduring curing, the silicone compound layers interact deeply with thepartially cured sleeve and become fully integral to provide a superiorsmooth contour and durable elastic inflatable balloon. The siliconecompound layers interact less deeply into a substantially fully curedsleeve and becomes less integrally bonded with the cured sleeve. Thefully cured sleeve does tend to have less residual adhesion with thesurface of the catheter during curing of the outer layers and istherefore more readily released. However, a sleeve ranging frompartially cured to fully cured provides the base element for theimproved inflatable silicone balloon, that does not require a releaseagent, and are each considered to be within the scope of the presentinvention.

After the catheters have cooled, the processing mandrels 34 are thenremoved from the inflation lumen by securely grasping the tip of thecatheter and easing the mandrels out with needle nosed pliers.

Referring now to FIGS. 10 and 11, the inflatable portion 32A of theballoon (defined by the length of the original sleeve 32), musttypically be slightly manipulated to release any residual adhesion thatoften occurs with the catheter during the curing process. Thismanipulation can be performed by hand; however, a release tool 44 wasdeveloped consisting of a one-quarter inch diameter stainless steel rod46 about six inches in length, having a handle on one end and having aone-half inch diameter polyvinylchloride (PVC) tubing 48 about twoinches in length mounted on the distal end of the rod. The rod is bentbehind the tubing at an angle of about 30 degrees upwardly, to provide acomfortable angle and hand clearance for the operator. The balloon isreleased from the catheter by placing the balloon 42 onto a flat rubbersurfaced fixture 50 where the tool is utilized to apply a small, gentleback and forth lateral force on the inflatable portion 32A whilesequentially rotating the catheter until the entire peripheral surfaceof the cylindrical inflatable portion is released from the catheter. Asshown particularly in FIG. 11, the lateral force and the friction of thetubing and the fixture creates a slight relative translation of theinflatable portion balloon material from the catheter material resultingis a progressive separation 50 between the materials. The catheter 20 isusually extruded with white silicone material, while the siliconeballoon material is typically transparent. The bonded shoulders of theballoon and the slightly adhered inflatable portion of the ballooninitially appear opaque white until the inflatable portion is released.After the inflatable portion is released, it appear clear andtransparent, to provide quality control and assurance that the releaseprocess has been successfully completed.

The tip of the distal end of the catheter is next trimmed to the desiredlength, which is typically determined by the use of calipers, and cutwith a pair of small hand held dikes, or a suitable automated cuttingdevice. The desired overall length of the catheter is similarly trimmedat the proximal end. Typical band markings, well known in the industry,are added from the distal end, every 10 cm over the length of thecatheter, to indicate to the physician during use, the length that thecatheter has been inserted into the vessel of the patient.

A suitable well know luer adapter tubing assembly (not shown) ispositioned onto the proximal end of the catheter, utilizing suitablewire processing mandrels to align and seal the lumens of the assemblyand catheter, while the assembly is securely bonded and sealed to thecatheter by a layer of Room Temperature Vulcanizing (RTV) siliconecompound. The luer adapter tubing assembly permits the lumens of thecatheter to be readily attached to mating luer devices such as syringesand fluid lines, for performing the medical or surgical procedure, aswell as for inflating and deflating the balloon. The luer adapter tubingassembly also provides a suitable handle on the proximal end of thecatheter, for rotating and manipulating the catheter during inserting,withdrawing and performing the medical procedures with the catheter.

Referring now to FIG. 12, the procedure is described for forming thedistal tip 54 of the catheter. For standard inflation lumen embolectomycatheters, RTV silicone compound is first transferred to a 3 cc syringehaving a dispensing needle. About 1 cc of RTV silicone compound isinjected into the inflation lumen(s) and a suitable small amount of RTVsilicone compound is injected to cover the distal end of the catheterand form a hemispherical dome thereon. Any excess RTV compound(extending beyond the diameter of the catheter) is removed by hand. Thesurface tension of the RTV compound tends to naturally form ahemispherical domed shape and the compound tends to cure rapidly afterapplication; but, if necessary, the RTV compound is easily manipulated(by finger tips or instruments) to form the desired smooth hemisphericaltip having a smooth transition with the diameter of the catheter, asshown in FIG. 12.

The distal tip for a biluminal (Foley type irrigation/drainage) catheteris similarly formed except that a suitable wire mandrel is inserted intothe primary lumen(s) 24 prior to applying the RTV compound, to insurethat each such lumen is not plugged during the tip forming process. Asuitable amount of RTV compound is then applied to the distal end andmanipulated into the desired tip configuration. The mandrel remains inthe catheter until the RTV tip has cured at room temperature for aboutan hour, and is then removed.

The tips of other specific catheters are similarly formed with RTVsilicone compound. Any additional distal or proximal irrigation ordrainage ports are suitably punched through the wall of the catheterinto the desired lumen.

The completely assembled catheter is illustrated in FIG. 13 withinflatable portion 32A inflated by fluid pressure applied through theinflation lumen 22 and port 30. The actual shape of the inflated portioncan be designed for a specific purpose of the catheter, by designing thelength of the sleeve 32, the elasticity and strength resulting from thesilicone compound, the thickness layer of the silicone balloon, and thepressure exerted on the inflation lumen.

Although a totally silicone catheter has specific functions andadvantages, the silicone balloon has also effectively been formed on aplastic catheter by applying a thin silicone layer on the surface of theplastic catheter. Plastic catheter materials, such as a nylon material,provide advantages in performing surgical and medical procedures wherestrength and rigidity greater than that of silicone may be desired. Adesign and method includes first applying a thin layer of uncuredsilicone dispersion compound over the plastic catheter over its entirelength, or at least over the area of the proposed silicone balloon andabout one inch beyond the end of a desired balloon location on thecatheter. The silicone layer is then placed in a curing oven at about125° C. for about 30 minutes, forming a substantially cured siliconesurface bonded over the plastic catheter. An inflation port is providedthrough the wall of the catheter communicating the inflation lumen withthe outer surface of the catheter in the area of the proposed balloon.The inflation port can be initially formed in the catheter and coveredduring the silicone coating step, or preferably punched after thesilicone coating has been formed on the surface of the catheter. Theinflatable balloon is then formed on the catheter over the inflationport, utilizing the previously described design and method to form aninflatable silicone balloon on the plastic catheter. Such a catheter canbe optimized having many desired properties of a plastic catheter, manyproperties and advantages of a silicone catheter, and the advantages ofan inflatable silicone balloon thereon.

While specific embodiments and examples of the present invention havebeen illustrated and described herein, it is realized that modificationsand changes will occur to those skilled in the art. It is therefore tobe understood that the appended claims are intended to cover all suchmodifications and changes as fall within the spirit and scope of theinvention.

We claim:
 1. A method of forming an inflatable silicone balloon having alength on a cured silicone catheter, with the catheter having an outerdiameter, an inflation lumen therein, and a lateral inflation port onthe distal end thereof communicating the inflation lumen with the outersurface of the catheter within the interior of the balloon, the stepscomprising:providing a substantially cured silicone compound sleeve,having an inner diameter corresponding to the outer diameter of thecatheter and having a length corresponding to the length of theinflatable balloon; positioning the sleeve onto the distal end of thecatheter and over the lateral inflation port; overdipping the distal endof the catheter including the sleeve into an uncured silicone dispersioncompound to a depth of about 0.25 inches beyond the sleeve, whereby thesleeve seals the inflation port and outer surface of the catheter fromcontact with the uncured silicone compound, forming an uncured siliconecompound layer over the catheter and the sleeve; drying the siliconecompound layer on the sleeve and catheter; curing the silicone compoundlayer and the sleeve on the catheter, whereby during curing, thecompound layer is securely bonded to the outer surface of the catheterand is bonded to the outer surface and ends of the sleeve, and the innersurface of the sleeve does not bond to the surface of the catheter; andreleasing the inflatable balloon from the catheter, by applying a seriesof lateral forces to the peripheral surface of the inflatable balloon,whereby the inner surface of the balloon is translated relative to thesurface of the catheter to thereby separate any residual adhesion of thesurfaces, thereby forming an inflatable silicone balloon over the lengthof the sleeve that is securely bonded to the catheter and can beinflated and deflated by pressure applied at the proximal end of theinflation lumen.
 2. The method as described in claim 1 further includingmultiple overdipping and drying steps prior to the curing step, furthercomprising:a least one additional overdipping of the distal end of thecatheter including the sleeve into the uncured silicone dispersioncompound to a depth of about 0.125 inches less than the previousoverdipping, forming an additional thickness of uncured siliconecompound layer over the catheter and the sleeve; and drying eachadditional thickness of uncured silicone compound layer; prior to curingthe uncured compound layer.
 3. The method as described in claim 2comprising a third overdipping step and a third drying step.
 4. Themethod as described in claim 2 wherein the drying step includes placingthe catheter in a drying environment at about 70° C. for about 20-30minutes.
 5. The method as described in claim 2 wherein the curing stepincluded placing the catheter in a curing environment at about 125° C.for about 45-60 minutes.
 6. The method as described in claim 2 furtherincluding a step of formulating the uncured silicone dispersion compoundprior to said overdipping step, further comprising:formulating acompound of about 85-95% by weight dimethyl silicone elastomerdispersion, in about 5-15% by weight xylene solvent and about 0.1-0.3%by weight crosslink catalyst, wherein the elastomer after curing has aShore A durometer greater than about
 30. 7. The method as described inclaim 6 wherein said formulating step comprises formulating the compoundof about 89.2% by weight dimethyl silicone elastomer dispersion, inabout 10.6% by weight xylene solvent and about 0.2% by weight crosslinkcatalyst.
 8. The method as described in claim 7 wherein said sleeveproviding step further comprises the steps:positioning a mandrel, havinga diameter corresponding to the diameter of the catheter, over thesilicone compound dipping the mandrel into the compound and withdrawingthe mandrel to form an uncured compound layer on the surface of themandrel; substantially curing the compound layer by placing the mandrelin a curing environment at about 125° C. for about 30-40 minutes;removing the substantially cured layer of sleeving from the mandrel; andcutting the sleeving into lengths, thereby providing the sleeve.
 9. Themethod as described in claim 8 wherein the curing step includes placingthe mandrel in the curing environment for about 30 minutes therebysubstantially, but not fully, curing the sleeving.
 10. The methoddescribed in claim 8 wherein the curing step includes placing themandrel in the curing environment for about 40 minutes therebysubstantially fully curing the sleeving.
 11. The method as described inclaim 8 wherein the removing the sleeving from the mandrel step includesthe step of covering the sleeving with a trichlortrifluoroethanesolution which expands the sleeving to facilitate removal from themandrel; and then after removing the sleeving from the mandreldissipating the solution whereby the sleeving is returned to it'soriginal size.
 12. The method as described in claim 8 wherein thedipping the mandrel step is performed at a rate of about 0.14 inches persecond into the compound, and is withdrawn from the compound at a rateof about 0.03 inches per second and forms a compound layer of about0.005 inches on the surface of the mandrel.
 13. The method of claim 7wherein the steps further comprises:the overdipping step including,positioning the distal end of the catheter over the uncured siliconecompound, and overdipping the catheter into the compound at a rate ofabout 0.14 inches per second, and withdrawing the catheter from thecompound at a rate of about 0.03 inches per second which thereby forms acompound layer of about 0.005 inches on the surface of the catheter eachtime the overdipping step is repeated; said drying step includingplacing the catheter in a drying environment at about 70° C. for about20 minutes; and said curing step including placing the catheter in acuring environment at about 125° C. for about 45-60 minutes.
 14. Themethod as described in claim 13 wherein said releasing step furtherincludes a releasing tool, comprising a rod having a handle on theproximal end thereof and having a plastic surface on the distal endthereof, adapted to apply the series of lateral forces to the peripheralsurface of the inflatable balloon.
 15. The method as described in claim8, further including the addition of a catheter tip utilizing a syringe,comprising the steps of:sealing the inflation lumen which extend to thedistal tip of the catheter with about 1 cc of Room TemperatureVulcanizing (RTV) silicone compound; applying RTV silicone compound tothe distal tip of the catheter until a hemispherical dome extends to thediameter of the catheter; removing any excess RTV compound that mayextend beyond the diameter of the catheter; drying the RTV compound atroom temperature with the distal end of the catheter in a verticalposition until the tip is stabilized.
 16. A method of forming aninflatable silicone balloon on a plastic catheter, the plastic catheterhaving an inflation lumen therein, an outer surface thereof and a distalend thereof, the steps comprising:applying a layer of uncured siliconedispersion compound over the distal end of the plastic catheterincluding at least the outer surface corresponding to the location andlength of the balloon on the catheter; curing the silicone compound,forming a cured silicone surface having an outer diameter bonded overthe outer surface on the distal end of the catheter; providing a lateralinflation port on the distal end thereof communicating the inflationlumen with the outer surface of the catheter; providing a substantiallycured silicone compound sleeve, having an inner diameter correspondingto the outer diameter of the catheter and having a length correspondingto the length of the inflatable balloon; positioning the sleeve onto thedistal end of the catheter with the length of the sleeve over thelateral inflation port; formulating a compound of about 85-95% by weightdimethyl silicone elastomer dispersion, in about 5-15% by weight xylenesolvent and about 0.1-0.3% by weight crosslink catalyst, wherein theelastomer after curing has a Shore A durometer greater than about 30,overdipping the distal end of the catheter including the sleeve into anuncured silicone dispersion compound to a depth of about 0.25 inchesbeyond the sleeve, whereby the sleeve seals the inflation port and outersurface of the cured silicone layer of the catheter from contact withthe uncured compound, forming an uncured silicone compound layer overthe catheter and the sleeve; drying the uncured silicone compound layeron the sleeve and catheter; curing the silicone compound layer and thesleeve on the catheter, whereby during curing, the overdipped compoundlayer is securely bonded to the outer surface of the catheter and isbonded to the outer surface and ends of the sleeve, and the innersurface of the sleeve does not bond to the surface of the catheter; andreleasing the inflatable balloon from the catheter, by applying a seriesof lateral forces to the peripheral surface of the inflatable balloon,whereby the inner surface of the balloon is translated relative to thesurface of the catheter to thereby separate any residual adhesion of thesurfaces, thereby forming an inflatable silicone balloon over the lengthof the sleeve that is securely bonded to the catheter and can beinflated and deflated by pressure applied at the proximal end of theinflation lumen.
 17. The method as described in claim 16 wherein theplastic catheter is a nylon material.
 18. A method of forming aninflatable silicone balloon having a length on a cured siliconecatheter, with the catheter having an outer diameter, an inflation lumentherein, and a lateral inflation port on the distal end thereofcommunicating the inflation lumen with the outer surface of the catheterwithin the interior of the balloon, the steps comprising:providing asubstantially cured silicone compound sleeve, having an inner diametercorresponding to the outer diameter of the catheter and having a lengthcorresponding to the length of the inflatable balloon; positioning thesleeve onto the distal end of the catheter over the lateral inflationport; formulating a compound of about 85-95% by weight dimethyl siliconeelastomer dispersion, in about 5-15% by weight xylene solvent and about0.1-0.3% by weight crosslink catalyst, wherein the elastomer aftercuring has a Shore A durometer greater than about 30, overdipping thedistal end of the catheter including the sleeve into an uncured siliconedispersion compound to a depth of about 0.25 inches beyond the sleeve,whereby the sleeve seals the lateral inflation port and outer surface ofthe catheter from contact with the uncured silicone compound, forming anuncured silicone compound layer over the catheter and the sleeve; dryingthe silicone compound layer on the sleeve and catheter; curing thesilicone compound layer and the sleeve on the catheter, whereby duringcuring, the compound layer is securely bonded to the outer surface ofthe catheter and is bonded to the outer surface and ends of the sleeve,and the inner surface of the sleeve does not bond to the surface of thecatheter; and releasing the inflatable balloon from the catheter, byapplying a series of lateral forces to the peripheral surface of theinflatable balloon, whereby the inner surface of the balloon istranslated relative to the surface of the catheter to thereby separateany residual adhesion of the surfaces, thereby forming an inflatablesilicone balloon over the length of the sleeve that is securely bondedto the catheter and can be inflated and deflated by pressure applied atthe proximal end of the inflation lumen.
 19. The method as described inclaim 18 further including multiple overdipping and drying steps priorto the curing step, further comprising:a least one additionaloverdipping of the distal end of the catheter including the sleeve intothe uncured silicone dispersion compound to a depth of about 0.125inches less than the previous overdipping, forming an additionalthickness of uncured silicone compound layer over the catheter and thesleeve; and drying each additional thickness of uncured siliconecompound layer; prior to curing the uncured compound layer.